The present invention is directed to a metallic beverage-type can end having a captively retained tear strip and pull tab attached thereto, and more particularly to a can end whereby venting of internal pressure contained in the can is ensured during initial lifting of the pull tab.
Many metallic cans for holding beverages or other liquid products are provided with easy open can ends, wherein a pull tab attached to a tear strip defined by a score line in the can end may be pulled to provide an opening in the can end for dispensing the can contents. For ecological and safety reasons, many areas now require that the tear strip and attached pull tab be retained to the can end after opening. In order to meet these requirements, various designs have been suggested by the prior art for ensuring that the tear strip and pull tab do not become separated from the can end. Generally, the pull tab is retained to the can end by means of a rivet or other similar attachment device. A recurring problem in the prior art, however, is that initial lifting of the pull tab oftentimes does not first fracture the score line immediately in front of the rivet attaching the pull tab to the can end. This initial action, referred to as "pop," vents or releases internal pressure in the can when beer or carbonated beverages are contained therein. If the venting action does not occur before continued lifting of the pull tab fractures the remainder of the score panel to complete the opening (known as "push"), it is possible that internal pressure in the can could cause the entire panel contained within the score line to blow out and expose the consumer to danger.
More specifically, the method of rivet development utilized in the prior art, such as found in U.S. Pat. Nos. 4,465,204 and 4,530,631 to Kaminski, et al., while successful, results in "loose metal" in the can end at the base of the rivet. By "loose metal," it is meant that such portions of can ends are flexible and may be deformed, or bent, with relative ease. During initial lifting of the pull tab, the rivet is forcibly tilted and the can end, specifically the metal around the rear side of the rivet base, is deformed. If tilting of the rivet is severe, opening of the can end in the area defined by the score line may occur simultaneously with the venting action described above, thereby causing the previously referred to blowout. Flexibility in the metal around the base of the rivet is also objectionable since, under pressure of the contents, the can end may bulge upward to the extent that the upper surface of the pull tab may rise above the chime of the seamed can, thereby impairing processing of the filled cans (pasteurization, casing, etc.). However, without the can end being flexible to allow deformation during lifting of the pull tab, undue stress can be placed on the rivet.